Upper gastrointestinal carcinomas (UGC) are a leading cause of cancer-related morbidity and mortality worldwide. Moreover, the incidences of proximal stomach, gastroesophageal junctional and esophageal adenocarcinomas are the fastest rising of any tumors in the United States and Western World. These tumors are characterized by a poor response to the present chemotherapeutic regiments and an overall low survival rate. The mechanisms of tumorigenesis in upper gastrointestinal tumors are unclear. p73, a new p53 family member, and its isoform deltaNp73 are increasingly recognized as key players in tumorigenesis, as well as in chemotherapeutic drug sensitivity. Upregulation of these p73 isoforms correlates with poor clinicopathological outcome in several types of tumors. However, in gastrointestinal tumors the role of the p73 gene remains unknown. Our preliminary results indicate that p73 and deltaNp73 transcripts and proteins are frequently overexpressed in UGC. At same time, these proteins have strong oncogenic effects in gastrointestinal cells, as has been demonstrated in our preliminary studies. Taken altogether, these data suggest that p73 and deltaNp73 may be involved in development or progression of UGC. We propose to delineate the role of p73 isoforms in upper gastrointestinal tumorigenesis. In addition, we aim to evaluate their clinical significance. Using a number of cellular and molecular biology techniques, we will characterize the interaction of p73 isoforms with other signaling pathways and investigate the mechanisms that regulate p73 gene expression. For the expression analysis of p73 isoforms in upper gastrointestinal carcinomas, we will employ a real-time RT-PCR analysis and immunohistochemical staining of tumor tissue arrays from our gastrointestinal cancer tissue bank. This information may provide new avenues for the development of novel prognostic and therapeutic targets. Our specific aims are: Aim 1: Characterize the clinical significance of p73 isoforms in upper gastrointestinal carcinomas. Aim 2: Characterize the biological functions of p73 isoforms in upper gastrointestinal adenocarcinomas. Aim 3: Investigate the regulation of p73 gene expression in upper gastrointestinal carcinomas.